Trailing blade



' Aug. 15, 1967 Filed June 6, 1966 P. A. VERKINDEREN ETAL 3,335,701

TRAILING BLADE 4 Sheets-Sheet 1 INVENTORS 7Z1 BY m, xii/424 ATTORNEYS Aug. 15, 1967 Filed June 6, 1966 P. A. VERKINDEREN ETAL. 3,335,701

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TRAILING BLADE Filed June 6, 1966 4 Sheets-Sheet 3 INVENTORS 51 @111 %MMM L/M M},

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Jaw. did, @441 aaw ATTORNEYS United States Patent 3,335,701 TRAILING BLADE Paul August Verkinderen, Edegem, and Jan Mullie, Wilrijk-Antwerp, Belgium, assignors to Gevaert-Agfa N.V., Mortsel, Belgium, 21 Belgian company Filed June 6, 1966, Ser. No. 555,366 Claims priority, application Great Britain, June 4, 1965, 23,988/65 12 Claims. (Cl. 118-247) This invention relates to a method and apparatus for metering and smoothing a liquid coating composition applied to a web.

The invention has been developed primarily for use in the manufacture of coated sheet materials for use in photographic processes. In that field of manufacture it is often necessary to coat webs with viscous coating compositions to form layers which must satisfy quite stringent conditions as regards uniformity of thickness and surface quality. As cases in point we refer to the formation of pigmented layers, subbing layers, anti-stress layers and layers sensitive to light or other radiation. In this specification the invention will therefore be more particularly described in relation to the manufacture of such materials but the invention can be applied in many other fields.

By way of preliminary explanation the term web as used in this specification denotes any flexible sheet material, e.g., plastics or paper, which can be continuously fed from a reel. The invention may be applied in the formation of a coating layer on top of a layer already formed with the aid of a similar or a different method and in such cases, the already formed coating or coatings is or are considered as part of the web,

The invention is not directly concerned with the particular way in which liquid composition is applied to the Web. This application may be performed in any conventional or other suitable manner and examples of suitable methods will be described. Rather, the invention is concerned with the subsequent stages of the coating method where excess coating composition is removed and the formed layer is smoothed. It is known to effect this metering and conditioning of the coating by a blade known in the paper industry and elsewhere as a trailing blade. This is a blade which is held so that it slopes towards the web in the direction of its advance, and so that thefree edge of the blade (extending transversely of the web) presses against the coated side of the web at a position where the latter runs over a backing roller with a resilient surface. The blade flexes very slightly under the contact pressure and the coated web moves progressively through the slot defined between the backing roller and the free edge portion of the blade.

The accurate setting of such trailing blades to form coatings free from defects is most difficult. In fact-such trailing blade devices have not been found suitable for use in the manufacture of photographic materials where the standards to be observed are particularly high. The slightest deformation .or damage to the blade edge results in defects in the coating. Moreover the smoothing action of the blade is poor and in consequence air bubbles (the so-called comets) are not thoroughly removed.

Now the present invention uses a type of trailing blade and is therefore related to the known trailing blade metering techniques but in the present invention the blade is arranged in a different manner, in particular the coated web is not gripped between the free blade edge and a backing member. A backing member is used but the pressure of the blade opposed by this backing member is exerted through a zone of a flexed blade set back from its free edge. The transverse margin of the blade extending between this zone and the free edge of the blade follows a part of the web course where the web is not positively supported and the web, as it leaves the backing member, is caused to follow a course parallel with this blade margin so that the latter exercises a smoothing action on the coating. The coating is metered, i.e., excess coating composition is squeezed off, at the zone where the coated web is sandwiched between the blade and the backing member.

It is surprising that this revised blade arrangement gives such improved results. In fact, the new method, while affording the advantages of the old trailing blade system that it can be used at high coating speeds and for metering coatings with particular rheological properties such as latices and slimy compositions, also affords the advantages that the setting of the blade to give accurate results is easy to perform, and the conditioning action of the blade in smoothing the coating is very good. It is also observed that Whereas the old trailing blade system tends to give very poor results when the applied coating has a thickness in excess of that equivalent to a coating weight of about 12 g./ sq. m. the present method gives good results even with layers comprising up to 50 grams of coating composition per square meter.

Broadly defined, the invention includes any method of metering and smoothing a liquid composition applied to a web to form a layer thereon, wherein the web bearing applied composition is conducted past a metering station where the web is supported by a backing member up to a well defined limit along the web path; a blade projecting from a blade holder and converging towards the web in its direction of travel is maintained flexed by pressure of the blade against the coated web where this is supported by said backing member adjacent said support limit, while leaving a free margin of the blade remote from said holder extending beyond such support limit; and the course of the web beyond said limit is such that'the coating is smoothed by said free blade margin.

The invention also includes apparatus constructed for performing a method as above defined.

The backing member for the web may be and preferably is in the form of .a roller, and this should have a smooth and preferably undeformable surface. In the old type of trailing blade device the backing member has necessarily to have a resilient covering and this is progressively deformed under the blade edge pressure as the roller rotates. The wear resistance of such rollers is not very good. In the present invention, the use of a roller with a slightly resilient coating is not excluded but resilience is not necessary and the backing roller preferably presents a non-resilient, e.g., polished metal, surface to the web.

The blade is preferably held between clamping members forming part of a blade holder which is mounted for bodily movement towards and away from the backing roller and also for angular movement for varying the angle at which the blade is inclined to the web.

The blade preferably makes contact with the coated web where this follows an upward course.

The invention will be further described by referring to the accompanying drawings in which FIG. 1 rep-resents diagrammatically one form of apparatus embodying the invention;

FIG. 2 is a diagrammatic sectional view showing enlarged the contact area of the web and the blade;

FIG. 3 is a graph showing the thickness of a coated layer as a function of some parameters;

FIGS. 4a to 40 show diagrammatically the application of the invention in various coating systems;

FIG. 5 is a sectional side view of an improved blade holder.

The coating apparatus as shown in its inoperative position in FIG. 1, is basically a dip coater, the coating composition in the pan being maintained at a level so as to coat the web only at one side.

The coater comprises a backing roller 11 to which a Web is fed by the roller 12 from a stock roll, a coating pan 13 containing a supply of coating composition 14 which is held, by any known means, e.g. an overflow, at a constant level 15 as indicated by a dash and dot line, and a roller 16 for guiding the web from the backing roller 11 to a following treating station destination, e.g. to a drying or gelling station, or to an other coating station.

The coating pan 13 is a double-wall type, the inner wall being represented in broken lines in the figure, wherein a heated liquid circulates between both walls for maintaining the coating composition at a pre-determined temperature.

The backing roller 11 is at each side rotatably journalled in a bearing 17 which is fixed on a horizontal support 18 next to the coating pan. The roller 11 has a diameter of 300' mm., and a length of 750 mm. It is made of steel and has been turned ofi", polished, hard chromiumplated and repolished so that its surface roughness amounts to only a few microns.

The trailing blade 20 consists of a strip of spring leaf steel which is cut from a roll of such material. It has a thickness of 0.4 mm., a width of 80 mm. and a length of 750 mm. It is clamped between the pressure members and 31, each of them substantially consisting of an elongate steel lath which has been planed to size and the facing sides of which have been polished.

The pressure member 30 is connected to the pressure member 31 by means of screws located in a transversely extending row. The screws pass through holes in the pressure member 30 and fit into threaded holes of the pressure member 31. The 'blade 20 is positioned by making it slide between the two opened pressure members until it abuts with its lower edge against the elongate spacer 32 having the same thickness as the blade, and which is seld in place by the screws 40 which pass through corresponding holes. The screws 40 are uniformly tightened by means of a torque-wrench and the blade is ready for a particular setting.

The pressure member 31 is supported by a blade support, in the present case the lever 25 which is rectangularly fitted to the lateral lower extremities of the pressure member 31.

The mechanism for adjusting the trailing blade 20 is also positioned on the support 18. This mechanism permits an adjustment of the blade in the horizontal direction, indicated by x, and an angular adjustment, indicated by 0c. The adjustment of the blade in the horizontal direction is done by displacing a member 19, provided near both transverse extremities of the blade, by rotating a threaded screw shaft 21 journalled in bearings 22, 23 which are fixed to the support 18. Upon rotation of the screw shaft 21 by means of the crank 24, the member 19 which is in threaded engagement with the screw shaft 21 moves towards or away from the roller 11. The angular position of the blade 20 is adjusted by means of the lever 25 which is pivotably connected at point 27 to the quadrant member 26 attached to the member 19. The member 26 is provided With a curved slot 28 and a threaded pin connected to lever 25 extends through this slot and carries a nut 29 by means of which the lever 25 can be clamped in any angular position.

As particularly appears from FIG. 2, the edge 38 of pressure member 30 is set back with respect to the edge 37 of pressure member 31. This permits the flexure of the blade under the contact pressure against the web to extend over a greater part of the blade width than would be possible if the member 30 were also to extend as close to the backing roller as does the member 31. Consequently, for a given blade curvature use can be made of a relatively stiff blade, which is less subject to damage or distortion than a thinner one. Even when using a very flexible blade, a uniform contact pressure exists over the length of the blade because the blade is supported by member 31 up to a position 37 which is very near to the position 39 at which the blade makes its first contact with the web. In practice, the bevelled top sides of the members 30 and 31, as well as their sides engaging the blade 20 are accurately and highly polished to ensure that the edges 37 and 38 of such members are true.

The roller 16 which determines the direction of the web course from the backing roller 11, is at each end rotatably journalled in a bearing 33 horizontally slidable in a support 34. The positions of the bearings 33 are controlled by a screw shaft 35 which can be rotated by the crank 36. The direction of the adjustment of the roller 16 is indicated by y.

The first contact between the blade 20 and the web occurs at the posiiton 39. The blade converges towards the web up to this position and it is here that the metering of the coating takes place in that the surplus deposit is arrested and flows back in the form of a curtain to the composition contained in the pan 13. A marginal portion of the blade extending up to its long free edge lies substantially flat and thus diverges from the backing roller surface. The roller 16 is adjusted horizontally so that as the web leaves the backing roller, it runs along this free marginal portion of the blade. Over the distance z the coating is spread and smoothed so that an extremely even texture of the coating is obtained. The distance 2 over which the blade contacts the web is preferably of the order of 5 to 15 mm.

In the known trailing blade devices the pressure of the blade adjacent the web is concentrated along the blade edge which therefore needs very careful machining. The slightest fault in this edge results in a non-uniform coating. The blade 20 in the illustrated machine is formed from inexpensive spring leaf steel and needs no machining. Moreover the correct setting of the blade does not require that skill which is necessary in setting the blade in the old type of trailing blade coaters. The smoothing effect of the blade in apparatus according to the invention is much greater than the blade in devices of the old type, and stripes and bubbles in the coated layer are effectively eliminated.

The thickness of the coating, or in the present case, the coat weight expressed in grams of coating composition applied per square meter of the web, depends on the following parameter: the contact pressure of the blade on the web, the angle of the blade, the viscosity of the coating composition and, to a minor extent, the speed of the web.

The expression angle of the blade is used to denote the inclination of the pressure members 30, 31 to the vertical direction, which is equivalent to the angle a between the lever 25 and the horizontal, because the lever 25 is normal to the said pressure members.

It has been observed that the adjustment of the angle a conveniently permits a rough control and the adjustment of the distance x permits a fine control of the coating thickness for a given coating viscosity and coating speed. 1 The effect of both said adjustments is illustrated in the graph of FIG. 3. The measured coat weight, when dried, is indicated in g./sq. m. and is plotted against the horizontal adjustment x of the blade holder for different settings of the angular adjustment or. The horizontal adjust- Water cc 6000 Gelatin g 600 Milk, as anti-foaming agent cc 300 2% aqueous solution of Leucophor B, an optical bleaching and brightening agent (C.I. 40,620),

marketed by Sandoz Ltd., Switzerland cc 210 56% aqueous suspension of barium sulphate kg 12 aqueous sodium hexametaphosphate cc 55 Tergitol 4-T, a wetting agent marketed by Union Carbide Corp., New York, 17, NY. cc 2 The composition has a relative density of 1.337 kg. per liter.

The smoothing of the coating is performed, as said already hereinbefore, by the extending front portion of the blade. It is clear that for each value of the parameters x and a, the position of the blade will change, the contact point 39 will rise or lower, and the direction of the portion of the blade extending over the distance z will change slightly. The said changes in the location of the point 39 and the direction of the blade are, however, rather small since the angle a is nearly always comprised between 15 and 30.

The correct setting of roller 16 is important. If the roller 16 is set too far to the left in the aspect of FIG. 1, a clearance will exist between the long free edge of the blade and the web, so that the smoothing of the coating will be considerably reduced, resulting into a plurality of parallel thin strips in the longitudinal direction of the web. If the roller 16 is set too far to the right, in the direction of the arrow y the web will exert a pulling movement on the said free edge of the blade and will tend to lift the blade from the roller so resulting into a non-uniform coating in the longitudinal direction of the web (the so-called shocks).

The apparatus illustrated by FIG. 1 is of course only an example. As one possible modification the means for holding the blade may be replaced by any type of blade holder well known per se in the art. Thus a holder may be used comprising a single member against which the blade is held by means of a vacuum created in spaces or cavities which are provided in such member, or the blade may be clamped between two pressure members which are urged together by vacuum. As another example, the blade may be magnetically held against one blade holder or between two blade holders by permanentor electro-magnets. Spacers in the form of thin elongate and flat metal strips, metal rods or wires for contacting the blade at relatively high pressure over a small surface or on a line or lines rather than over the entire surface of the blade holder may be introduced between the blade and the pressure members.

Instead of the illustrated blade holder adjustment mechanism the blade holder may be brought hydraulically; pneumatically or by an electric servo-motor system from the inoperative position into the operative or an intermediate position as will be explained further in the description.

The blade itself can also be of diiferent form from that described with reference to FIGS. 1 and 2. Instead of being made out of spring leaf steel, it may be made out of other metals, e.g. bronze or stainless steel, in certain applications. Further the blade may have a decreasing stiffness towards its trailing edge, which property may be obtained by using a blade the thickness of which is reduced towards its, trailing edge, or by providing several blades of smaller width at the clamped margin of the blade to form a laminated structure. Occasionally the blade itself may have a laminated structure. It is to be noted, however, that in many cases very good, and even the best, results will be obtained by a simple and inexpensive blade as described in the embodiment of FIG. 1.

Preferably the length of the blade is equal to that of the backing roller. In this way the parts of the periphery of the roller extending beside the web which is passed over it, are freed from coating composition so that it cannot tend to seep around the edges of the web and deposit on the back side of the web. The length of the blade may, however, be also smaller than the length of the backing roller, and in case the risk exists that the coating composition would be applied to the back side of the web, edge doctors or dams in the coating pan may be provided for restricting the width over which the coating is applied.

In operation, the blade requires no special care or treatment. Owing to the particular positioning of the blade it lasts very long, and its life exceeds many times the life of the commonly used trailing blades.

When a new coating operation is started, one proceeds as follows. The coating pan and the backing roller are cleaned and dried. The web is passed through the apparatus as shown in FIG. 1. The trailing blade, which has been put in a position spaced from the backing roller, is cleaned, dried and briefly polished with fine sanding paper at its side facing such roller. The angle a and the adjustment y are set according to the coating composition which will now be applied, and the adjustment x is set so as to let the blade just touch the uncoated web. The coating composition is put in the pan and the apparatus is started. Immediately thereafter the distance x is reduced so as to obtain the desired setting for a particular coat weight.

The object of the described adjustment of the blade, prior to coating, is to make the operation start in the best conditions. If the blade remains spaced from the web as the coating starts, an excessive quantity of coating composition becomes applied to the web, giving rise to dirtying of parts of the installation and to difiiculties in drying. If the blade is at the final setting of x as the coating starts, there is a risk of the blade tearing fibers off the uncoated web. The detached fibers may be withheld by the front edge of the blade, and thereby give rise to stripes and irregularities in the coating. According to an alternative way of starting the coating operation the adjustment x is initially set so that a zone of the blade set well back its long free edge bears against the uncoated web where it is backed by the roller but so that the bearing pressure is insuflicient to flex the blade to bring the long free edge of the blade into the final straight line path of the web. In this initial position the blade slightly displaces the web from such path. When the coating has started to flow beneath the blade the blade holder is moved nearer to the backing roller so that the blade flexes into the correct final position.

As already indicated, the backing roller need not have a hard and uudeformable surface. The invention can, e.g., be carried out by modifying an existing trailing blade water of the old type, embodying a resiliently covered backing roller, by changing the blade and installing means for adjusting the course of the Web from the backing roller. The web will then be supported on a resilient backing layer. Although it is certainly possible to obtain good results in working in this way, it is not recommended because of the liability of the resilient layer to suffer damage or non-uniform wear.

A great number of other known arrangements may 'be used for applying the coating to the Web. These arrangements may be provided with one or more systems for preor postmetering the applied coating.

According to a first modified embodiment, the level of the composition in the pan 13 of FIG. 1 may be lowered so that the composition only contacts the web through a meniscus of coating composition. This techni'que is known as the meniscus or bead coater. Other coating systems are illustrated in FIGS. 40 to 40.

FIG. 4a shows a kiss-coater wherein the roller 50, applying the coating composition 53 to the web 51, rotates in the same direction as the web travel. The metering and the smoothing of the coated layer occur by the trailing blade 52 according to the invention, the web being supported by the free-rotating backing roller 54, and the web travel being adjusted by the displaceable roller 55. The composition removed from the web by the trailing blade 52 flows in the pan 56 and is returned to the coating pan 57 by the pump 58.

The applicator roller 50 also has an eflect on the coat weight in that by increasing or reducing its peripheral speed in respect of the speed of web travel, more or less coating is applied to the Web.

FIG. 4b shows a reverse roller coater using two rollers 60 and 61 mounted side by side and rotating in opposite directions. The roller 60 dips into the coating composition 63 which is maintained at a constant level in the coating pan. A first control of the coat weight is provided by adjusting the gap between the two reverse running rollers, and by regulating their peripheral speeds. A second control of the coat weight and the smoothing of the coating are performed by the trailing blade 65 according to the invention, the course of the web past the trailing blade being adjusted by displaceable roller 66.

FIG. 4c shows a two roller coater, the roller 70 dipping in the coating composition 71 and applying it to the web 72 in the direction of the web travel, the other roller 73 being a backing roller. A first control of coat weight is provided by the adjustment of the gap, respectively the pressure, of the roller 70 in respect of the roller 73. A second control of the coat weight and the smoothing of the coating are performed as hereinbefore described by means of the adjustable trailing blade 74 and displaceable roller 75. As in each other embodiment, also the viscosity of the coating composition is determinant in the coat weight.

In connection with the application of the coating composition to the web, it may be pointed out that the transfer of the composition from its supply onto the web may be assisted or achieved in a known way by an electrostatic field which extends from the supply of coating composition to an electrically conductive member or part which is close to or in contact with the back side of the web. In another way, the web may be electrostatically charged and the composition be given a charge of opposite polarity. When the coating composition contains magnetizable particles, e.g. in the manufacture of magnetic recording material, the electrostatic field may advantageously be replaced by a magnetic field of force.

In coating a web with an apparatus according to the present invention, it is also possible to submit the coated material to an after-treatment such as stretching, buffing, calendering.

Finally, optical measuring means such as infrared, ultraviolet and visible radiation means, electrical measuring means such as capacitive, inductive and resistive means, radiographic measuring means, such as X-ray and ,B-ray, may be provided for continuously or cyclically measuring the thickness of the coating and for controlling by means of a servo-mechanism the adjustment of the trailing blade (x, and/or on and y), so as to obtain a uniform coating thickness in the longitudinal direction of the web.

The following example illustrates the improvements which have been obtained in coating a latex containing baryta layer to a paper support, according to the present invention.

First it will be described how one commonly proceeds for coating determined baryta compositions. Thereafter will be described how the same compositions can be applied according to the invention.

To a paper web of 135 g./sq. m., three layers are successively applied.

A first layer is applied at a coat weight of 32.5 g./sq. m. (dried coating) by means of a so-called Jagenberg coater, i.e. a coating apparatus wherein the coating composition is applied to the web by means of two reverse-rotating rollers which pre-meter the coating and wherein the applied coating is post-metered by means of an air-knife, at a coating speed of 70 m./min., from the following composition:

Water cc 850 Gelatin g 600 56% aqueous suspension of barium sulphate kg 12 10% aqueous sodium hexametaphosphate cc 200 Water cc 2500 Gelatin g 300 56% aqueous suspension of barium sulphate kg 12 10% aqueous sodium hexametaphosphate cc 1360 Milk, as anti-foaming agent cc 450 Ethyl alcohol cc 1320 40% aqueous dispersion of a copolymer consisting of 66% ethyl acrylate units, 20% vinyl isobutyl ether units, 12% styrene units and 2% acrylic acid units g 750 The composition has a relative density of 1.32 kg. per liter, and a time of outflow of 15.5 sec.

A third layer is applied thereon at a coat weight of 15 g./sq. m., by means of a brush coater, at a coating speed of m./min., from the following composition:

'Water Gelatin g 600 5 6% aqueous suspension of barium sulphate kg 12 10% aqueous sodium hexametaphosphate cc 1300 Milk cc 300 The composition has a relative density of 1.35 kg. per liter, and has a time of outflow of 15.5 sec.

The total coat weight which has thus been applied to the web, amounts to 60 g./sq. m.

The apparatus according to the invention permits to coat the mentioned compositions in only two layers which, moreover, have a greater relative density. Other improvements resulting from the use of the trailing blade arrangement will be described hereinafter.

A first layer is applied at a coat weight of 30 g./ sq. m. by means of the trailing blade coater as shown in FIG- URE 1. The angle on amounts to 20, the parameters x and y are adjusted as a function of the coat weight and the quality of the coating. The composition is as follows:

Gelatin g 300 70% aqueous suspension of barium sulphate kg 9.6 20% aqueous sodium hexametaphosphate cc 100 Milk, as anti-foaming agent cc 450 40% aqueous dispersion of a copolymer consisting of 66% ethyl acrylate units, 20% vinyl isobutyl ether units, 12% styrene units and 2% acrylic acid units g 750 Adjupal A, conc., an alkylphenol polyglycolic ether wetting agent marketed by Adjubel N.V., at Lembeek-Halle, Belgium cc The composition has a relative density of 1.86 kg. per liter, and is characterized by a time of outflow of 36 see. A second layer is applied thereon at a coat weight of 30 g./sq. m. by means of the same trailing blade coater, from the following composition:

20% aqueous sodium hexametaphosphate ..cc 3000 Milk or 300 Adjupal A, conc. 170

The composition has a relative density of 1.60 kg. per liter, and has a time of outflow of 37 sec.

The second method of coating shows the following ad vantages over the first one:

(1) The compositions may be applied in two steps instead of in three steps, as mentioned already hereinbefore, which means a considerable gain of time. The coating of the compositions in two layers was formerly impossible, since, on the one hand the mentioned Jagenberg coater is not appropriate for coating latex-containing compositions and, onthe other hand, the coating together of the former first and second layers by means of the brush-coater is only feasible at a coat weight of at most 20 g./sq. m. whereas the first layer need already be coated at 32.5 g./sq. m.

(2) The surface of the coatings is smoother than that of coatings applied by the conventional coaters. This is especially interesting in the manufactureof photographic printing material which after processing is hotglazed.

(3) The former (second) latex containing layer can now be coated as the first layer, and at a weight of 30 g./sq. m. instead of at 12.5 g./sq. 111. More latex and less gelatin is thus present, reducing the curling tendency and the brittleness of the photographic material.

(4) The former top (third) layer, required for the good adhering of the photographic emulsion layer, is now coated at 30 g./ sq. 111. instead of at 15 g./sq. m. and has thereby an increased efiiciency.

(5) Both layers show a greater relative density, or in other words contain less water, so that for the same dry coat weight less water must evaporate in drying. This means that the existing drying installations may be used at higher speed.

The examples given hereinbefore particularly relate to the coating of photographic baryta coatings. The invention can, however, be used for coating many other liquid compositions.

The invention can be applied, e.g. for applying photographic emulsions, antistress layers, anti-halation layers and colour filters in the production of photographic material, for the coating of zinc oxide and similar photoconductive layers in the production of electrophotographic recording material, for the coating of thermosensitive layers in the production of thermophotographic recording material, for the coating of image-receiving layers in the production of image-receiving materials suitable for use in silver halide diffusion transfer processes, for thec'oating of electrically conductive layers on supports with very good insulating properties in the production of electrostatic recording material, for the coating of stripping layers in the production of photographic stripping films for use in photomechanic reproduction processes, for the coating of magnetizable layers in the production of magnetic recording tape, for the coating of subbing layers, for the production of X-ray film, and for the coating of plastics, paints and resins on flexible supports (which themselves may or may not be plastics), for coating webs with layers from compositions containing starch, latices, etc.

Hereinafter another embodiment of the pressure members and of the blade support will be described which constitutes an improvement over the arrangement shown in FIG. 1.

The arrangement, a side view of which is shown in FIG. 5, comprises generally a blade support 89 and a blade holder which for clearness sake have been drawn separated from each other. The blade holder 90 comprises the movable pressure member 91, and the pressure stationary member 92 whichis bolted to an elongate L-shaped member 93. The blade support 89 is composed of the elongate square beam 94 to which at each extremity a flange 95 is fitted which has an extending; end journal 96 by means of which it is journalled in the bearing of a movable carriage (not shown). In the present embodiment, the square beam had a length of 150 'cm., and was provided with a central boring with a diameter of 5 cm. in order to reduce its weight, and reduce thereby the bending in the longitudinal direction to about 0.01 mm. The blade holder 90 is reproducibly fitted with its underside 97 to the top side of the square beam 94 by means of a series of bolts each located next to the other in the longitudinal direction of the parts. The object of the removable and reproducible fitting of the blade holder to the blade support is to provide a simple system which permits the quick and easy replacement of a blade. One or more spare blade holders are provided, in which a blade has been positioned and accurately tightened. In case the replacement of a blade of the coater is required, the operators simply replace the blade holder 90 by a spare unit, and no further adjustments of the parameters x and cc are needed since it is sure that the position taken by the new blade exactly corresponds to the one taken by the removed blade.

In the present embodiment, also the clamping of the trailing blade has been improved. This is performed by the leg 98 which rectangularly projects from the pressure member 91 and which slides in the groove formed by the parts 92 and 93.

It should be noted that the faces of both parts which are in sliding engagement are exactly parallel to each other and highly polished. They, moreover, are exactly normal to the sides which engage the trailing blade 100.

Besides the guiding of the movable pressure member 91, the said leg 98 also considerably increases the stiffness of the said member.

The result is that the clamping faces of the pressure members are always exactly parallel to each other, and an even tensioning of the bolts passing through the openings 99 (shown in broken lines) which are ranged next to each other in the longitudinal direction of the blade holder, causes a uniform clamping of the blade 100.

We claim:

1. Apparatus for use in metering and smoothing a liquid composition applied to a web to form a layer thereon comprising means for conveying a web through coating and metering stations; a backing member located so as to afford support for a said web (after application of coating compositions thereto), up to a Well defined limit along the web path; a blade mounted on. a blade holder and capable of being maintained by such holder in a position in which the blade is flexed by pressure of the blade against a web where supported by said backing member adjacent said limit, while leaving a free margin of the blade remote from said holder extending beyond such limit in the direction of web travel; and means enabling the course of a said Web, along that part of its path which immediately follows such limit, to be adjusted to lie in juxtaposed parallel relationship with said free blade margin when the blade is in said flexed condition.

2. Apparatus according to claim 1, wherein the said backing member is in the form of a rotatable backing roller. 1

3. Apparatus according to claim 2, wherein the said backing roller has a smooth and undeformable surface.

4. Apparatus according to claim 2, wherein said means for adjusting the course of a web comprises a displaceable and freely rotatable roller over which such a web can travel.

5. Apparatus according to claim 1, wherein the blade 11 holder comprises clamping members which clamp the blade between them and wherein the clamping member which is on that side of the blade which is concave when the blade is flexed by pressure against a web, extends nearer to the free edge of the blade than the clamping member on the other side of the blade.

6. Apparatus according to claim 5 wherein the blade holder is mounted on a carriage so that the holder can be moved bodily towards and away from the backing rnember along a predetermined path and can also be swung about an axis for varying the angle of the blade relative to aweb.

7. Apparatus according to claim 1 wherein the blade holder comprises clamping members which clamp the blade between them, and wherein such members have tongue and groove sliding engagement affording accurate guidance of such members during the relative displacements thereof which occur when the clamping pressure is adjusted.

8. Apparatus according to claim 1, wherein the blade holder is readily removable together with a blade therein, from a mounting, so as to facilitate replacement of holder and blade as a unit.

9. Apparatus according to claim 1, wherein the blade holder is arranged so that in use, the blade contacts 2 a web where it follows an upward course.

10. Apparatus according to claim 6, wherein the angular position of the blade is used to roughly adjust the coating thickness.

11. Apparatus according to claim 6, wherein the lateral 5 displacement of the blade towards and away from the support is used to finely adjust the coating thickness.

12. Apparatus according to claim 6, wherein in the direction of the lateral displacement of the blade towards the support two positions of the blade are provided, a

10 first position wherein the blade is slightly removed from the support and which is used to start coating, and a second position which is less remote from the support than the first one and which is taken when coating has started.

5 CHARLES A. WILLMUTH, Primary Examiner.

R. SMITH, Examiner. 

1. APPARATUS FOR USE IN METERING AND SMOOTHING A LIQUID COMPOSITION APPLIED TO A WEB TO FORM A LAYER THEREON COMPRISING MEANS FOR CONVEYING A WEB THROUGH COATING AND METERING STATIONS; A BACKING MEMBER LOCATED SO AS TO AFFORD SUPPORT FOR A SAID WEB (AFTER APPLICATION OF COATING COMPOSITIONS THERETO), UP TO A WELL DEFINED LIMIT ALONG THE WEB PATH; A BLADE MOUNTED ON A BLADE HOLDER AND CAPABLE OF BEING MAINTAINED BY SUCH HOLDER IN A POSITION IN WHICH THE BLADE IS FLEXED BY PRESSURE OF THE BLADE AGAINST A WEB WHERE SUPPORTED BY SAID BACKING MEMBER ADJACENT SAID LIMIT, WHILE LEAVING A FREE MARGIN OF THE BLADE REMOTE FROM SAID HOLDER EXTENDING BEYOND SUCH LIMIT IN THE DIRETION OF WEB TRAVEL; AND MEANS ENABLING THE COURSE OF A SAID WEB, ALONG THAT PART OF ITS PATH WHICH IMMEDIATELY FOLLOWS SUCH LIMIT, TO BE ADJUSTED TO LIE IN JUXTAPOSED PARALLEL RELATIONSHIP WITH SAID FREE BLADE MARGIN WHEN THE BLADE IS IN SAID FLEXED CONDITION. 